Java Object Serialization Specification
version 1.5.0

Change History

July 24, 2004 Updates for Java^TM 2 SDK, Standard Edition, v1.5 Beta 1

Added support for serializing enum constants.

Added specification of class modifier flags used in the computation of default serialVersionUID values to Section4.6 Stream Unique Identifiers".

Aug. 16, 2001 Updates for Java^TM 2 SDK, Standard Edition, v1.4 Beta 2

Added support for class-defined readObjectNoData methods, to be used for initializing serializable class fields in cases not covered by class-defined readObject methods. See Section3.5 The readObjectNoData Method", as well as Appendix A, "Security in Object Serialization".

New methods ObjectOutputStream.writeUnshared and ObjectInputStream.readUnshared provide a mechanism for ensuring unique references to deserialized objects. See Section2.1 The ObjectOutputStream Class", Section3.1 The ObjectInputStream Class", as well as Appendix A, "Security in Object Serialization".

Documented new security checks in the one-argument constructors for ObjectOutputStream and ObjectInputStream. See Section2.1 The ObjectOutputStream Class" and Section3.1 The ObjectInputStream Class".

Added caution against using inner classes for serialization in Section1.10 The Serializable Interface".

Clarified requirement that class-defined writeObject methods invoke ObjectOutputStream.defaultWriteObject or writeFields once before writing optional data, and that class-defined readObject methods invoke ObjectInputStream.defaultReadObject or readFields once before reading optional data. See Section2.3 The writeObject Method" and Section3.4 The readObject Method".

Clarified the behavior of ObjectInputStream when class-defined readObject or readExternal methods attempt read operations which exceed the bounds of available data; see Section3.4 The readObject Method" and Section3.6 The readExternal Method".

Clarified the description of non-proxy class descriptor field type strings to require that they be written in "field descriptor" format; see Section6.2 Stream Elements".

July 30, 1999 Updates for Java^TM 2 SDK, Standard Edition, v1.3 Beta

Added the ability to write String objects for which the UTF encoding is longer than 65535 bytes in length. See Section6.2 Stream Elements".

New methods ObjectOutputStream.writeClassDescriptor and ObjectInputStream.readClassDescriptor provide a means of customizing the serialized representation of ObjectStreamClass class descriptors. See Section2.1 The ObjectOutputStream Class" and Section3.1 The ObjectInputStream Class".

Expanded Appendix A, "Security in Object Serialization".

Sept. 30, 1998 Updates for JDK^TM 1.2 Beta4 RC1

Documentation corrections only.

June 22, 1998 Updates for JDK^TM 1.2 Beta4

Eliminated JDK^TM 1.2 java.io interfaces, Replaceable and Resolvable.
References to either of these classes as an interface should be replaced with java.io.Serializable. Serialization will use reflection to invoke the methods, writeReplace and readResolve, if the Serializable class defines these methods. See Section2.5 The writeReplace Method" and Section3.7 The readResolve Method."

New javadoc tags @serial, @serialField, and @serialData provide a way to document the Serialized Form of a Serializable class. Javadoc generates a serialization specification based on the contents of these tags. See Section1.6 Documenting Serializable Fields and Data for a Class."

Special Serializable class member, serialPersistentFields, must be declared private. See Section1.5 Defining Serializable Fields for a Class."

Clarified the steps involved in computing the serialVersionUID in Section4.6 Stream Unique Identifiers."

Feb. 6, 1998 Updates for JDK^TM 1.2 Beta 3

Introduced the concept of STREAM_PROTOCOL versions. Added the STREAM_PROTOCOL_2 version to indicate a new format for Externalizable objects that enable skipping by an Externalizable object within the stream, even when the object's class is not available in the local Virtual Machine. Compatibility issues are discussed in Section6.3 Stream Protocol Versions."

The ObjectInputStream.resolveClass method can return a local class in a different package than the name of the class within the stream. This capability enables renaming of packages between releases. The serialVersionUID and the base class name must be the same in the stream and in the local version of the class. See Section3.1 The ObjectInputStream Class."

Allow substitution of String or array objects when writing them to or reading them from the stream. See Section2.1 The ObjectOutputStream Class" and Section3.1 The ObjectInputStream Class."

Sept. 4, 1997 Updates for JDK^TM 1.2 Beta1

Separated the Replaceable interface into two interfaces: Replaceable and Resolvable. The Replaceable interface allows a class to nominate its own replacement just before serializing the object to the stream. The Resolvable interface allows a class to nominate its own replacement when reading an object from the stream.

Modified serialization to use the JDK^TM 1.2 security model. There is a check for SerializablePermission "enableSubstitution" within the ObjectInputStream.enableReplace and ObjectOutputStream.enableResolve methods. See Section2.1 The ObjectOutputStream Class" and Section3.1 The ObjectInputStream Class."

Updated writeObject's exception handler to write handled IOExceptions into the stream. See Section2.1 The ObjectOutputStream Class."

July 3, 1997 Updates for JDK^TM 1.2 Alpha

Documented the requirements for specifying the serialized state of classes. See Section1.5 Defining Serializable Fields for a Class."

Added the Serializable Fields API to allow classes more flexibility in accessing the serialized fields of a class. The stream protocol is unchanged. See Section1.7 Accessing Serializable Fields of a Class," Section2.2 The ObjectOutputStream.PutField Class," and Section3.2 The ObjectInputStream.GetField Class."

Clarified that field descriptors and data are written to and read from the stream in canonical order. See Section4.1 The ObjectStreamClass Class."

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